The default settings for the lighting on and around the runways is often very unrealistic. Some airports ae visible at long distance just because of the bright VASI lights. On the other hand, when having to land in low visibility conditions, like heavy fog, seeing the approach lighting on time is very helpfull.
The specific changing of the brightness can be accomplished with entries in the FSX.cfg, or Prepar3D.cfg files. These files in Windows7/8 are located in: C:\users\ Name\AppData\Roaming\Microsoft\FSX C:\users\ Name\AppData\Roaming\Lockheed Martin\Prepare3D
When this cfg file is opened in NotePad the following lines can be inserted in the section: